AISI 4320H Alloy Steel (UNS H43200)

Topics Covered

Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations


Alloy steel contains alloying elements such as aluminum, chromium, copper, titanium, nickel, silicon and manganese in varying amounts to manipulate the properties of steel such as weldability, strength, formability, hardenability and corrosion resistance.

AISI 4320H is a nickel-chromium-molybdenum steel. The following section will discuss about AISI 4320H alloy steel.

Chemical Composition

The chemical composition AISI 4320H alloy steels is outlined in the following table.

Element Content (%)
Iron, Fe 95.745 - 97.18
Nickel, Ni 1.55 - 2
Manganese, Mn 0.40 - 0.70
Chromium, Cr 0.35 - 0.65
Molybdenum, Mo 0.20 - 0.30
Carbon, C 0.17 - 0.23
Silicon, Si 0.15 - 0.30
Sulfur, S ≤0.040
Phosphorous, P ≤0.035

Physical Properties

The following table shows the physical properties of AISI 4320H alloy steels.

Properties Metric Imperial
Density 7.85 g/cm3 0.284 lb/in3

Mechanical Properties

The mechanical properties of AISI 4320H alloy steels are displayed in the following table.

Properties Metric Imperial
Tensile strength 1505 MPa 218300 psi
Yield strength 1050 MPa 152000 psi
Modulus of elasticity 1225 GPa 177700 psi
Bulk modulus 140 GPa 20300 ksi
Shear modulus 80 GPa 11600 ksi
Poisson’s ratio 0.29 0.29
Elongation at break 13.50% 13.50%
Reduction of area 48.20% 48.20%
Hardness, Brinell 429 429
Hardness, Vickers 455 455
Hardness, Knoop 461 461
Hardness, Rockwell C 46 46
Hardness, Rockwell B 105 105

Thermal Properties

The thermal properties of AISI 4320H alloy steels are given in the following table

Properties Metric Imperial
Thermal expansion co-efficient (@-18-95°C/-0.4-203°F) 11.3 µm/m°C 6.28 µin/in°F
Thermal conductivity 44.5 W/mK 309².°F

Other Designations

Other designations that are equivalent to AISI 4320H alloy steels include the following.

  • ASTM A304
  • SAE J1268
  • AMS 6299


The following are the list of applications of AISI 4320H alloy steels:

  • Heavy-section gears
  • Pinions
  • Other heavy-duty machinery components

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